Crude oils and other heavier petroleum fractions often contain paraffinic materials. The major constituents of these paraffinic waxes contain long-chain normal alkyl regions. These waxy compounds readily crystallize out upon cooling of the oil fraction containing them. This cooling may result in deposits which obstruct the flow of hydrocarbon production fluids if the cooling occurs in a flowline such as a pipe or other conduit. These deposits must be removed from the flowlines and vessels to achieve continued and/or efficient production of petroleum. These deposits may also occur in the near-wellbore region of the formation, well production tubing, valves and chokes, flowlines, risers, surface treating vessels, and storage tanks. Tank bottoms are often a combination paraffin, asphaltene, emulsion, and/or inorganic scale.
Various methods for removing paraffin wax have been utilized in the past. Sulfur trioxide has been used to contact the paraffin and form a dispersible material that is removed with an aqueous liquid and a surfactant. Other solvents and dispersants such as a copolymer of a primary alcohol and ethylene oxide with sodium silicate and N-substituted succinimide ethers have been tried. U.S. Pat. No. 4,813,482 teaches injecting a mixture of an alkyl or aralkyl polyoxyalkylene phosphate ester surfactant in free acid form or as a salt with a mutual solvent and water to remove paraffin deposits. This mixture must be at a temperature greater than the melting point of the wax to be effective. Since none of these processes melt the wax, they can only slowly eat away at its surface. This is not fast enough at most realistic surface-to-volume ratios. Furthermore, they create dispersions in water which must be disposed of or otherwise expensively dealt with.
U.S. Pat. No. 4,755,230 teaches the use of inorganic nitrate/nitrite compounds in redox reactions which result in an exotherm which melts the paraffin deposit and generates nitrogen gas. This technique does melt the wax, but requires the use of water to deliver the reactants, so that if the wax disperses at all, which it may well not, it does so into water which then must be expensively dealt with. Furthermore, gas generating redox reactions tend to be self accelerating, rendering them at best kinetically unpredictable, and at worst explosive.
Methods for removing paraffin wax deposits from the surfaces of hydrocarbon (oil and/or gas) production equipment during oil production by melting and subsequently dispersing the deposits are also described in U.S. Pat. No. 5,484,488. These methods utilize an acid compound and a neutralizer compound which react exothermally to melt the deposit and form a dispersant to remove the melted fragments of the deposit. Examples of acids used in this method include H3PO4, H2SO4, and HCl, whereas examples of neutralizers used include NaOH, KOH, MgO, MgCO3 and NaHCO3.
Asphaltene deposits in hydrocarbon production equipment also cause problems and must be removed. Asphaltenes are organic materials consisting of aromatic and naphthenic ring compounds containing nitrogen, sulfur and oxygen molecules. The asphaltene fraction of crude may be defined as the organic part of the oil that is not soluble in straight-chain solvents such as pentane or heptane. Asphaltenes may exist as a colloidal suspension stabilized by resin molecules (e.g. aromatic ring systems) in the oil. The asphaltenes may precipitate as a result of a number of effects or factors including, but not necessarily limited to, pressure drop, shear forces (turbulent flow), acids, solution carbon dioxide (CO2), mixing of incompatible crude oils, injected condensate, or other conditions or materials that break or disturb the stability of the asphaltic dispersion. Asphaltene deposits may also occur in the near-wellbore region of a subterranean formation, well production tubing, valves and chokes, flowlines, risers, surface treating vessels, and storage tanks.
It would thus be desirable to discover a new method and/or composition to remove paraffins, asphaltenes and other types of undesired deposits and impediments from the near-wellbore region of a subterranean formation, hydrocarbon production equipment and the like that may be easily implemented.